# Consider the reactions:

Question:

Consider the reactions:

(a) $\mathrm{H}_{3} \mathrm{PO}_{2}$ (aq) $+4 \mathrm{AgNO}_{3}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{I}) \rightarrow \mathrm{H}_{3} \mathrm{PO}_{4}(\mathrm{aq})+4 \mathrm{Ag}(\mathrm{s})+4 \mathrm{HNO}_{3}(\mathrm{aq})$

(b) $\mathrm{H}_{3} \mathrm{PO}_{2}$ (aq) $+2 \mathrm{CuSO}_{4}$ (aq) $+2 \mathrm{H}_{2} \mathrm{O}$ (I) $\rightarrow \mathrm{H}_{3} \mathrm{PO}_{4}$ (aq) $+2 \mathrm{Cu}$ (s) $+\mathrm{H}_{2} \mathrm{SO}_{4}$ (aq)

(c) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHO}(\mathrm{l})+2\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}(\mathrm{aq})+3 \mathrm{OH}^{-}(\mathrm{aq}) \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COO}^{-}(\mathrm{aq})+2 \mathrm{Ag}(\mathrm{s})+4 \mathrm{NH}_{3}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})$

(d) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHO}(\mathrm{l})+2 \mathrm{Cu}^{2+}(\mathrm{aq})+5 \mathrm{OH}^{-}(\mathrm{aq}) \rightarrow$ No change observed.

What inference do you draw about the behaviour of $\mathrm{Ag}^{+}$and $\mathrm{Cu}^{2+}$ from these reactions?

Solution:

$\mathrm{Ag}^{+}$and $\mathrm{Cu}^{2+}$ act as oxidising agents in reactions (a) and (b) respectively.

In reaction (c), $\mathrm{Ag}^{+}$oxidises $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHO}$ to $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COO}^{-}$, but in reaction (d), $\mathrm{Cu}^{2+}$ cannot oxidise $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHO}$.

Hence, we can say that $\mathrm{Ag}^{+}$is a stronger oxidising agent than $\mathrm{Cu}^{2+}$.